I've done a design consisting of white spray paint onto wood, followed by drawing with a "Sharpie" brand permanent marker.

The sharpie despite being described as "permanent on most surfaces" was not exactly on top of the white spray paint (It faded significantly over time so the contrast was lost between the original dark black and white background - to a greyish colour against a white background).

I re-did the drawing and tried to spray it with a clear spray paint after the marker had dried for two days, to try and add a protective coat to stop the marker colour fading so much (sealing it from air).

When I sprayed it, the ink ran dramatically, blurring the drawing. I sprayed it slowly at a reasonable distance from the wood, but it still blurred.

Is there any other way I can stop the marker fading over time? Other clear protective coatings for example?